Microscale devices such as integrated circuits (ICs), optoelectronic, micromechanical, micro-electro-mechanical, and microfluidic devices contain micron- and sub-micron-sized features that are formed according to a precise sequence of fabrication steps and under tightly-controlled process conditions. Often a substrate such as a semiconductor wafer is provided, which contains active and passive electrical circuit elements such as transistors, resistors and capacitors. Semiconductor and thin-film deposition techniques are performed to change layers or add layers to the substrate. The layers added to the substrate or portions thereof can be permanent, as in the case of a conductive plane or electrode, an insulative barrier between conductive planes, a light-conductive waveguide, a structural layer used to form a micromechanical component, or an etchstop for controlling the effects of an etching process. Other layers or portions of layers can be temporary, as in the case of an intermediate sacrificial layer formed between the substrate and a structural layer that is subsequently removed to release such structural layer or a portion thereof from the substrate, or in the case of a photoresist layer formed on the substrate as a template for the creation of electronic or mechanical features. Many of the above-described layers are subjected to a removal process such as etching (which can occur isotropically, or anisotropically along a desired direction) to either completely remove the layer or to form: (1) features such as apertures, vias, microchambers, microfluidic channels, and trenches; (2) two-dimensional structures such as contacts, electrical leads, optical windows, and deflectable membranes; or (3) three-dimensional structures such as actuators and cantilevers. The removal of layers or portions of layers can also be accomplished by chemomechanical polishing or other surface micromachining techniques. The starting substrate employed during a fabrication process, for example a silicon or glass substrate, can itself be subjected to a bulk micromachining technique to form cavities or apertures therein. Additionally, transient layers such as photoresist materials can be removed in-part by development and in-whole by chemical stripping or by plasma ashing.
During the course of a fabrication process, one or more cleaning steps can be required to remove various types of contaminants or other undesired materials, or to otherwise prepare a surface for subsequent deposition of layers. For example, the top surface of a bulk starting material such as a substrate might initially be oxidized. The oxidation can render the surface of the substrate incompatible with a subsequent deposition procedure, in which case the oxidation would need to be removed in preparation for the deposition of an additional layer onto the substrate surface. In another example, the deposition of a metal layer onto a semiconductor substrate might require a preceding desorbing step to degas the substrate. Moreover, the removal of a photoresist layer, after a plasma ashing process for example, might leave residue, thereby requiring a cleaning step to remove such residue. In addition, the formation of micron-sized features such a deep trenches by etching might result in residues or particulates requiring removal. Polishing and planarization processes are other sources of residual contaminants. Various cleaning media have been employed. Of particular recent interest is the use of supercritical carbon dioxide (CO2) to clean a substrate surface in a contained environment such as a processing chamber.
Many of the steps required during the course of a fabrication process occur within chambers or modules that are hermetically sealed from the ambient environment during use so as to maintain desired process conditions (e.g., pressure, temperature, electric field strength, flow rate). Depending on the particular process step being carried out, such chambers or modules are maintained at reduced pressure (e.g., plasma-enhanced deposition), atmospheric or near-atmospheric pressure (e.g., atmospheric pressure and low pressure chemical vapor deposition). Most deposition processes, however, are conducted in controlled atmospheres at reduced pressure, while conventional cleaning processes are conducted at ambient or near-ambient pressures (e.g., 0-20 pounds per square inch “gauge”, psig). The respective facilities used for deposition and cleaning processes are separate, thus conventionally requiring that a given substrate be transferred from a deposition chamber to a remotely situated cleaning facility. Accordingly, the overall fabrication process flow is discretized, and usually requires that the substrate be exposed to the ambient environment in the interval between pre-cleaning and deposition, or between deposition and post-cleaning.
It would therefore be advantageous to provide a method and apparatus that enables substrates to be cleaned in a contained environment under conditions that are optimal for the cleaning process (e.g., high pressure), while at the same time integrates the cleaning process with the fabrication processes (which require different sets of optimal conditions) in a compatible manner, and without the need to transfer the substrate through the ambient environment.